The Standard Electrical Dictionary / A Popular Dictionary of Words and Terms Used in the Practice of Electrical Engineering

by T. O'Conor Sloane

Fig. 33. NOBILI'S PAIR.

FIG. 34. VERTICAL PAIR ASTATIC COMBINATION.
Astatic Needle.
A combination of two magnetic needles so adjusted as to
have as slight directive tendency as possible. Such a pair of needles
when poised or suspended will hardly tend to turn more to one point of
the compass than another. The combination is generally made up of two
needles arranged one above the other, with their poles in opposite
directions. This combination is usually called Nobili's pair. If of
equal strength and with parallel magnetic axes of equal length they
would be astatic. In practice this is very rarely the case. A resultant
axis is generally to be found which may even be at right angles to the
long axis of the magnets, causing them to point east and west. Such a
compound needle requires very little force to turn it one way or the
other. If one of the needles is placed within a coil of insulated wire a
feeble current will act almost as strongly to deflect the system as if
the other was absent, and the deflection will only be resisted by the
slight directive tendency of the pair of needles. This is the basis of
construction of the astatic galvanometer. Sometimes coils wound in
opposite directions and connected in series, or one following the other,
surround both needles, thus producing a still greater effect of
deflection.
Other astatic needles are shown in the cuts below. [Figures 33 to 35.]
51 STANDARD ELECTRICAL DICTIONARY.

FIG. 35. SIMPLE ASTATIC NEEDLE.
Asymptote.
A line continuously approached by a curve, but which the curve, owing to
its construction or nature of curvature, can never touch, be tangent to,
or intersect.
Atmosphere.
(a) A term applied to the atmospheric pressure as a practical unit of
pressure equal to 15 lbs. to the square inch as generally taken. It is
really about 14.7 lbs. per square inch, or 1,033 grams per square
centimeter.
(b) Air, q. v.
Atmosphere Residual.
The atmosphere left in a vessel after exhaustion. The term may be
applied to any gas. In an incandescent lamp after flashing the residual
atmosphere consists of hydro-carbons.
Atmospheric Electricity.
The electricity of the atmosphere, rarely absent, but often changing in
amount and sign. Benjamin Franklin, in a memoir published in 1749,
indicated the method of drawing electricity from the clouds by pointed
conductors. In June, 1752, he flew a kite and by its moistened cord drew
an electric spark from the clouds, confirming his hypothesis that
lightning was identical with the disruptive discharge of electricity. To
observe electricity in fine weather a gold-leaf or other electroscope
may be connected to the end of a long pointed insulated conductor. The
electricity during thunderstorms can be shown by a similar arrangement,
or burning alcohol or tinder gives an ascending current of warm air that
acts as a conductor. Quite elaborate apparatus for observing and
recording it have been devised. Atmospheric electricity is usually
positive, but occasionally negative. When the sky is cloudless it is
always positive, increasing with the elevation and isolation of the
place. In houses, streets, and under trees no positive electricity can
be found. In the Isle of Arran, Scotland, a rise of 24 to 48 volts per
foot of increase in elevation was found by Sir William Thomson. At
sunrise the electrification of the air is feeble, it increases towards
noon and decreases again to reach a second maximum a few hours after
sunset. It increases with the barometric pressure generally. In cloudy
weather it is sometimes negative and the sign often changes several
times in the same day. In a thunderstorm the changes in sign and
potential are very rapid. The cause of atmospheric electricity is far
from clear. Tait attributes it to a contact effect between air and water
vapor, Solmeke to friction of water vesicles against ice particles in
the upper atmosphere, he first showing that the two may coexist. The
cause of the enormous increase of potential producing lightning is
attributed to the decreased capacity due to the change of water from
cloud vesicles to drops, thus diminishing the electrostatic capacity of
the water in question. (See Lightning.)
52 STANDARD ELECTRICAL DICTIONARY.
Atom.
The ultimate particle or division of an elementary substance; the
smallest part that can exist in combination, and one which cannot exist
alone. An elementary substance is composed of molecules just as truly as
a compound one, but the atoms in the molecule of an elementary substance
are all precisely alike. Hence atoms are the units of chemistry, they
have to do with combinations, but the physical unit, the smallest
particle of matter that can have an independent existence, is the
molecule. The two are often confounded, especially by writers of a few
years ago, so that by "atom" the molecule is often meant. There is
nothing to be said of their size or mass. All such calculations refer to
the molecule, q. v., often spoken of and called the atom.
[Transcriber's note: Yet to be discovered: electron--1897 (5 years),
proton--1920 (28 years), neutron--1932 (30 years), quark--1961 (69 years).]
Atomic Attraction.
The attraction of atoms for each other, in virtue of which they combine
into molecules; chemical affinity, q. v., treats principally of this,
although molecular attraction also plays a part in it.
Atomic Heat.
The product of the atomic weight of a substance by its specific heat.
This product is approximately the same, 6.4; this approximation is so
close that it is of use in determining the valency and atomic weights of
substances. The atomic weight of a substance therefore represents the
approximate number of gram-calories required to raise one gram-atom, q.
v., of such substance through 1° C. (1.8° F.)
Atomicity.
The quantivalence or valency of the atoms; the number of combination
bonds, or bonds of affinity, possessed by the atoms of any substance.
Thus two atoms of hydrogen combine with one atom of oxygen, and three of
oxygen with one of sulphur, forming saturated compounds. Therefore,
taking hydrogen as of single atomicity or a monad, oxygen is of double
atomicity or a dyad, and sulphur is of six-fold atomicity, or a hexad.
The elements are thus classified into seven orders of atomicities, thus:
1, Monads or Univalent elements, Hydrogen, etc.
2, Dyads or Bivalent " Oxygen, etc.
3, Triads or Trivalent " Nitrogen, etc.
4, Tetrads or Quadrivalent " Lead, etc.
5, Pentads or Quinquivalent " Phosphorous, etc.
6, Hexads or Sexivalent " Chromium, etc.
7, Heptads or Septivalent " Chromium, etc.
The same element often possesses several atomicities. Barium is
generally a dyad, sometimes a tetrad; nitrogen acts as a monad, dyad,
triad, tetrad and pentad. The familiar electrolysis of water, giving two
volumes of hydrogen to one of oxygen, is one of the illustrations of the
theory indicating that two atoms of hydrogen are combined with one of
oxygen.
53 STANDARD ELECTRICAL DICTIONARY.
Atomic Weight.
The number expressing the relative weight of the atom of any substance,
that of hydrogen being generally taken as unity. This is the universal
system, although any other element might be taken as the basis of the
system. The whole theory of atomic weights is based on the
indivisibility of the atom and on the theory of atomicity, q. v. (See
Equivalents.)
[Transcriber's note: The standard is now the isotope carbon-12 as
exactly 12.]
Attraction.
The tendency to approach and adhere or cohere, shown by all forms of
matter. It includes gravitation, cohesion, adhesion, chemical affinity
and other forms, and is opposed by repulsion, and is sometimes overcome
by it, although it may be assumed to be always present. See the
different kinds of attractions under their titles: Atomic Attraction,
Electro-magnetic Attraction and Repulsion, Electro Static Attraction and
Repulsion, Electro-dynamic Attraction and Repulsion; Magnetic Attraction
and Repulsion; Molar Attraction.
Audiometer.
An apparatus for obtaining a balance of induction from two coils acting
upon a third. The third is placed between the other two and is free to
move towards either. A scale is provided to show the extent of its
movement. A varying or interrupted current being passed through the two
outer coils, the preponderating current will produce the most induction
if the central coil is equidistant. It can always be moved to such a
point that there will be no inductive effect, one counteracting the
other. Thus its position measures the relative induction. A telephone is
in circuit with the intermediate coil and is used to determine when its
position is such that no current is induced in it. It is sometimes used
as a direct test of hearing. (See Hughes' Induction Balance.)
Synonym--Acoutemeter.
Aura, Electrical.
The blast of air produced at highly electrified points.
Aurora.
A luminous display seen in the northern heavens in the northern
hemisphere, where it is the Aurora Borealis, and seen in the southern
heavens in the southern hemisphere, where it is called Aurora Australis,
or indifferently for either, the Aurora Polaris. It takes the form of
pale luminous bands, rays and curtains varying in color. Near the poles
they are very numerous. A French commission observed 150 auroras in 200
days. Their height is variously estimated at from 90 to 460 miles; they
are most frequent at the equinoxes and least so at the solstices. There
is a secular variation also, they attain a maximum of occurrence every
11 years together with sun spots, with a minimum 5 or 6 years after the
maximum. There is also a period of 60 years, coincident with
disturbances in the earth's magnetism. Various attempts have been made
to account for them. They have a constant direction of arc with
reference to the magnetic meridian (q. v.) and act upon the magnetic
needle; in high latitudes they affect telegraph circuits violently.
There is a strong probability that they represent electric currents or
discharges. De la Rive considers them due to electric discharges between
the earth and atmosphere, which electricities are separated by the
action of the sun in equatorial regions. According to Balfour Stewart,
auroras and earth currents.(q. v.) may be regarded as secondary currents
due to small but rapid changes in the earth's magnetism. The subject is
very obscure. Stewart treats the earth as representing the magnetic core
of an induction coil, the lower air is the dielectric, and the upper
rarefied and therefore conducting atmosphere is the secondary coil. This
makes the aurora a phenomenon of induced currents. Then the sun may be
regarded as the instigator of the primary changes in the earth's lines
of force representing the primary of an induction coil.
[Transcriber's note: Solar wind, streams of electrons and protons,
interacting with the earth's magnetic field causes aurora. Neither
electrons (1897) nor protons (1920) were known in 1892. The Soviet
satellite Luna first measured the solar wind in 1959. Even today
increased understanding of solar and auroral phenomenon continues.]
54 STANDARD ELECTRICAL DICTIONARY.
Austral Pole.
The north pole of the magnet is thus called sometimes in France; the
austral pole of a magnet is the one which points towards the north polar
regions As unlike magnetic poles attract each other, it is but rational
to call the north-seeking pole of the magnet the south or Austral Pole.
In the same nomenclature the south pole of a magnet, or the
south-seeking pole, is called the Boreal Pole.
A. W. G.
Abbreviation for American Wire Gauge, q. v.
Axis, Electric.
The electric axis of a pyroelectric crystal, such as a tourmaline
crystal; the line connecting the points of greatest pyroelectric
excitability.
Axis of Abscissa.
In a system of rectilinear, or right angle co-ordinates, the horizontal
axis. (See Co-ordinates.)
Synonym--Axis of X.
Axis of Ordinates.
In a system of rectilinear right angle co-ordinates, the vertical axis.
(See Co-ordinates.)
Synonym--Axis of Y.
Azimuth.
The angle between the plane of the meridian and the plane of an azimuth
circle, q. v.
Azimuth Circle.
A great circle, whose plane passes through the zenith or point of the
heavens directly overhead; any great circle in whose plane the vertical
at the point of observation is included.
Each celestial body has or determines an azimuth circle.

55 STANDARD ELECTRICAL DICTIONARY.
B.
(a) Abbreviation for Baumé, a hydrometer scale. (See Baumé.) Thus 10º B.
means "ten degrees Baumé."
(b) Symbol for the coefficient of induced magnetization, or the number
of lines per square centimeter induced in a magnetic circuit or in any
specified part of it.
B. A.
Abbreviation for British Association. It is prefixed to standards fixed
by the committee of the British Association for the Advancement of
Science. Thus the B. A. ohm means the British Association ohm, a measure
of resistance which is equal to the resistance of a column of mercury
104.9 centimeters long and one square millimeter area of cross-section.
(See Ohm.)
Back Induction.
A demagnetizing force produced in a dynamo armature when a lead is given
the brushes. The windings by such setting of the brushes are virtually
divided into two sets, one a direct magnetizing set, the other a cross
magnetizing set. The latter have a component due to the obliqueness of
the neutral line, which component is demagnetizing in its action.
Back Shock or Stroke of Lightning.
A lightning stroke received after the main discharge of the lightning,
and caused by a charge induced in neighboring surfaces by the main
discharge. The discharge affects the evenness of distribution of
surrounding surfaces so that a species of secondary discharge is
required to make even the distribution, or to supply charge where needed
to bind an opposite one. The effects are much lese severe as a rule than
those of the main charge, although the back stroke has caused death. The
back stroke is sometimes felt a considerable distance from the place of
the original lightning stroke.
Synonym--Return Stroke.
Back Stroke.
(a) In telegraphy the return stroke of the lever in a telegraph sounder,
striking the end of the regulating screw with a sound distinct from that
which it produces on the forward stroke as it approaches the magnet
poles. It is an important factor in receiving by ear or sound reading.
(b) See Back Shock or Stroke of Lightning.
Balance.
(a) Wheatstone's Bridge, q. v., is sometimes termed the Electric
Balance.
(b) A suspension or torsion balance is one which includes a filament or
pair of filaments to whose lower end or ends are attached a horizontal
indicator often called a needle, or a magnetic needle. (See Torsion
Balance.)
(c) See Induction Balance, Hughes'.
(d) For Thermic Balance, see Bolometer.
(e) See Balance, Ampere.
56 STANDARD ELECTRICAL DICTIONARY.
Balance, Ampere.
A class of electrical measuring instruments due to Sir William Thomson
may be grouped under this head.
The instrument is a true balance or scales such as used for weighing. It
is supported by a torsional wire support in place of knife edges. At
each end it carries a circle of wire through which the current to be
tested is passed. The torsional wire support enables the current to be
carried to these wire rings. Above and below each of these rings are two
similar rings, also connected so as to receive the current. They are so
connected that the current shall go through them in opposite senses.
When a current passes, therefore, one of these rings repels and one
attracts the balanced ring.
The extent of this action measures the intensity of the current. A
sliding weight moving along a graduated scale on the balance is used to
bring the balance beam into equilibrium when the current is passing. The
degree of displacement of this weight gives the strength of the current
in amperes.
These balances are made for different currents. Thus there is a
centi-ampere balance, deka-ampere balance and others, as well as an
ampere balance.
Balata.
A gum used as an insulating material. It is the inspissated juice of a
sapotaceous tree, the bullet tree, Mimusops globosa, of tropical
America, from the Antilles to Guiana. It is intermediate in character
between caoutchouc and gutta percha. It is superior to gutta percha in
some respects, being very slightly acted on by light.
Synonym--Chicle.
B. & S.. W. G.
Abbreviation for Brown & Sharpe Wire Gauge; the regular American Wire
Gauge. (See Wire Gauge, American.)
Barad.
An absolute or fundamental unit of pressure, equal to one dyne per
square centimeter.
Barometer.
An apparatus for measuring the pressure exerted by the atmosphere. It
consists, in the mercurial form, of a glass tube, over 31 inches long,
closed at one end, filled with mercury and inverted, with its open end
immersed in a cistern of mercury. The column falls to a height
proportional to the pressure of the atmosphere from 30 to 31 inches at
the sea level. The "standard barometer" is a height of the mercury or of
the "barometric column" of 30 inches or 760 centimeters, measured from
the surface of the mercury in the cistern.
The column of mercury is termed the barometric column. Above it in the
tube is the Torricellian vacuum.
[Transcriber's note: More accurately, 29.92 inches of mercury or 14.696
PSI.]
Bars of Commutators.
The metal segments of a commutator of a dynamo or motor. They are made
of bars of copper, brass or bronze insulated from one another. (See
Commutator.)
Synonyms--Segments, Commutator Segments, Commutator Bars.
57 STANDARD ELECTRICAL DICTIONARY.
Bath.
(a) In electro-plating the solution used for depositing metal as
contained in a vat or tank; as a silver, copper, or nickel bath used for
plating articles with silver, copper, or nickel respectively.
(b) In electro-therapeutics a bath with suitable arrangements,
electrodes and connections for treating patients with electricity. It is
termed an electric bath or electro-therapeutic bath.
Bath, Bipolar Electric.
In electro-therapeutics a bath in which the electrodes are both immersed
in the water. The patient placed between them receives part of the
discharge. The electrodes are large copper plates, termed shovel
electrodes.
Bath, Electric Shower.
An electro-medical shower bath. The patient is placed on a metallic
stove or support connected to one of the electric terminals. Water
slightly alkaline is showered upon him. The other electrode is in
connection with the water. The rain of drops and streamlets is the
conductor of the current or discharge.
Bath, Multipolar Electric.
An electro-medical bath with a number of electrodes instead of two.
Bath, Stripping.
In electro-plating a solution used for dissolving and thus removing the
plating from any object. The stripping bath is of the same general type
as the plating bath for the same metal as the one to be dissolved. The
object to be "stripped" is made the anode of a plating circuit, and as
the current acts the old plating is attacked and dissolves, leaving the
body of the article bare. It is simply the operation of plating
reversed. The same term is applied to baths acting by simple solution.
Stripping baths are described under the different metals as Silver Bath,
Stripping--Gold Bath, Stripping.
Bath, Unipolar Electric.
An electro-medical bath, in which only one electrode connects with the
water of the bath. The second electrode is supported above the bath. The
patient touches this while in the water whenever electric action is
desired.

FIG. 36. THREE WIRE MOULDING OR BATTEN.